Trace sampling

ABSTRACT

A trace sampling detection system includes a gathering device configured to gather particles through a handle-bar, a gate and an air-stream gatherer. The handle-bar includes collection holes positioned to be adjacent to a user&#39;s hand when the user grips the handle-bar, and is configured to dislodge and capture particles from the user&#39;s hand when the user grips and moves the handle-bar. The gate includes a series of collection holes, is positioned to be adjacent to the user&#39;s clothing when the user traverses the gate, and is configured to dislodge and capture particles from the user&#39;s clothing in response to pressure applied from the user. The air-stream gatherer includes an outward vent and an in-drawing vent, and is positioned to enable objects, such as the user&#39;s feet, to be placed between the outward and in-drawing vents. The air stream is configured to dislodge and capture particles from objects, such as the user&#39;s feet, that block the air-stream between the vents. A collection tube is configured to deposit gathered particles from the gathering device onto a portion of a sample media. A carousel wheel that includes the sample media is configured to rotate the sample wheel such that the portion of the sample media including the gathered particles is presented to an exothermic decomposition detector that detects, through an infrared sensor, the decomposition of the gathered particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. patent application Ser. No. 11/425,313, filed Jun. 20, 2006, andtitled “Trace Sampling” which claims priority from U.S. ProvisionalApplication Nos. 60/691,778, filed Jun. 20, 2005, and titled “SimplifiedTrace Sampling of People For Explosives”; 60/700,039, filed Jul. 18,2005, and titled “Simplified Trace Sampling of People For Explosives”;60/702,616, filed Jul. 27, 2005, and titled “Trace Explosives DetectorBased Upon Detecting Exothermic Decomposition”; 60/743,083, filed Dec.29, 2005, and titled “Energetic Material Detector For Explosive TraceDetection”; and 60/743,402, filed Mar. 3, 2006, and titled “EnergeticMaterial Detector For Explosive Trace Detection.” Each of theseapplications is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to trace sampling to detect materials such asexplosives.

BACKGROUND

In order to detect the presence of a material, such as explosives,particles of the material may be collected and analyzed.

SUMMARY

In one general aspect, a trace sampling detection system includes agathering device configured to gather particles through each of severalcomponents. A handle-bar includes collection holes positioned to beadjacent to a user's hand when the user grips the handle-bar. Thehandle-bar is configured to dislodge and capture particles from theuser's hand when the user grips and moves the handle-bar. A gateincluding a series of collection holes is positioned to be adjacent tothe user's clothing when the user traverses the gate. The gate isconfigured to dislodge and capture particles from the user's clothing inresponse to pressure applied from the user. An air-stream gathererincluding an outward vent and an in-drawing vent is positioned to enableobjects, such as the user's feet, to be placed between the outward andin-drawing vents. The air-stream is configured to dislodge and captureparticles from objects, such as the user's feet, that block theair-stream between the outward and in-drawing vent. A collection tube isconfigured to deposit gathered particles from the gathering device ontoa portion of a sample media. A carousel wheel that includes the samplemedia is configured to rotate the sample wheel such that the portion ofthe sample media including the gathered particles is presented to anexothermic decomposition detector. An exothermic decomposition detectoris configured to detect, through an infrared sensor, the decompositionof the gathered particles.

Implementations may include one or more of the following features. Forinstance, the collection holes may be tapered, and may have sharp edgesconfigured to scrape a surface that contacts them.

The handle-bar may be configured to move in a radial motion. Thehandle-bar may include a conductivity sensor configured to detect thepresence of skin. The conductivity sensor may be configured to determineif two hands are being used to grip the handle-bar.

Also, the gate may be shaped with a curve that is designed to conform tothe shape of part of a human body. The gate may swing out only when thehandle-bar is moved. The movement of the gate, or the concurrentmovement of the gate and of the handle-bar, may present a path for theuser to traverse. Either the gate or the handle-bar, or both, may employless resistance to movement for slow movements than for quick movements.

The analyzing system may be configured to detect particles other thanexplosive particles.

The system may also include a blower to create the vacuum in thecollection holes and the in-drawing vent, and the air pressure for theoutward vent. One blower may be used for the collection holes in thehandle-bar and the gate, and the in-drawing vent, and a second blowermay be used for the outward vent.

In another general aspect, a trace sample detection system includes agathering device configured to gather particles through at least two ormore of a handle-bar, a gate, and an air-stream gatherer. The handle-barincludes collection holes positioned to be adjacent to a user's handwhen the user grips the handle-bar, and the gate includes a series ofcollection holes positioned to be adjacent to the user's clothing whenthe user traverses the gate. The air-stream gatherer includes an outwardvent and an in-drawing vent positioned to enable objects to be placedbetween the outward and in-drawing vents. An analyzing device isconfigured to analyze gathered particles from the gathering device forproperties that are indicative of the presence of particles of explosivematerials.

Implementations may include one or more of the features noted above.

In another general aspect, trace sampling detection includes gatheringparticles through two or more of a handle-bar, a gate and an air-streamgatherer, and analyzing the gathered particles for properties that areindicative of the presence of particles of explosive materials.

In another general aspect, a trace sampling detection system includes agathering device configured to gather particles through one or morecollection holes and an impact collector configured to deposit gatheredparticles onto a portion of a sample media. The system also includes acarousel wheel including the sample media. The carousel wheel isconfigured to rotate the sample wheel such that the portion of thesample media including the deposited gathered particles is presented toan exothermic decomposition detector. The system further includes anexothermic decomposition detector configured to detect, through aninfrared sensor, decomposition of heated materials.

Implementations may include one or more of the following features. Forinstance the carousel wheel may be configured to heat the sample mediaresistively. The sample media may be configured to be resistively heatedby running a current through the sample media. The sample media may beconfigured such that the same portion of the sample media may be reusedthrough multiple exposures to the impact collector and the exothermicdecomposition detector. The exothermic decomposition detector may beconfigured to heat the sample media radiatively. The carousel wheel maybe replaced with a reel-to-reel mechanism.

In a further general aspect, a transportation mechanism for a particledetection system that includes a gathering device, an impact collectorconfigured to deposit gathered particles, and an exothermicdecomposition detector configured to detect decomposition of a depositedmaterial includes a carousel wheel including a sample media configuredto accept a deposit of material from the impact collector. The carouselwheel is configured to rotate the sample wheel such that the portion ofthe sample media including the deposited gathered particles is presentedto the exothermic decomposition detector.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B, and 1C illustrate views of an exemplary collection devicefor collecting samples of material.

FIG. 2 illustrates an exemplary hand sampler.

FIG. 3 illustrates an exemplary impact collector.

FIGS. 4A and 4B illustrate a top and side view of an exemplary collectorand detection system.

FIGS. 5A and 5B illustrate data results of particle detection.

FIG. 6 illustrates a method of detecting particles.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

People who handle or work with explosives, drugs, or other materialstypically become contaminated with trace residue of the materials. Forexample, explosive particles may remain on the hands followingmanufacturing and/or handling of a bomb or explosive material, and someof these particles are may be transferred to the person's clothing, suchas the front pockets and the fly area of the person's pants. Such traceresidue may also be transferred onto items such as wallets, spectacles,keys, purses, and door handles, and serves to re-contaminate the hands,even when they are washed and the person changes clothing.

In order to thwart sample collection methods such as pressing a buttonor ticket, or atmospheric testing, a contaminated person may takeprecautions, such as washing of the hands immediately prior to enteringa security checkpoint. Sampling material from multiple locations on anindividual's body while applying a shearing force to release particlesincreases the difficulty of thwarting such detection attempts.

Sampling techniques described in this document will work in a variety ofsituations and locations. For example, the sampling techniques may beemployed with train and aircraft passengers, as well as at otherlocation where it is necessary to prevent the transport of explosives orother materials, or to determine if someone has handled explosives orother materials. The trace sampling technologies are not limited by manytemperature extremes, and can be installed in a broad range ofoperational environments, indoor or outdoor.

Although the following discussion is directed to explosive detection,other particles may be detected. Specifically, the system and methodsdiscussed below may be used to gather, collect, and detect hazardouschemicals, illicit drugs, chemical and/or biological warfare agents, orother materials that may leave trace particles. Further, although thefollowing discussion is directed towards people, many of the techniquesdescribed below could be used to detect other objects with minimaladjustment. For example, luggage on a conveyer belt could be sentthrough a similar turnstile system with minor modifications to thesamplers.

Referring to FIGS. 1A-1C, a collection device 100 includes materialcollection mechanisms in an explosive trace sampling and detectionturnstile system. The collection device 100 includes pedestals 105 and106, an entrance 107, an exit 109, a hand sampler 110, a torso or waistsampler 120, and a shoe sampler 130 with sampling techniques directed toeach corresponding area of the body.

In the device 100, passengers traverse a passage which is defined by thepedestals 105 and 106. The passage includes an entrance 107, awalkthrough space including the samplers 110-130, and an exit 109. Invarious implementations, the entrance 107 or exit 109 is presented bythe motion of the hand and torso samplers 110 and 120. Each of thesamplers 110-130 includes collection holes which draw in materials suchas explosive particles for analysis. Each of the samplers 110-130 mayalso include an associated movement or action designed to increase thenumber of particles that will be gathered. With sufficient pressure andshear force, explosive particles will be extracted from the hand, torso,or shoe areas. In particular, the hand and torso samplers 110 and 120dislodge and collect samples of material through contact, and the shoesampler employs a directional air stream to dislodge particles frompants, cuffs, and shoes, and push the particles to the shoe sampler 130.

The collection device 100 may be integrated into a small-profilewalkthrough turnstile, as shown in FIGS. 1A-1C. As a passenger passesthrough the turnstile, the collection device 100 automatically screens apassenger's hands, torso, and feet for trace explosives.

In the implementation shown, the passenger pushes the hand sampler 110down to unlock the turnstile gate that includes the torso sampler 120.When the passenger grasps the hand sampler 110 at grips 115, suction inthe interior of tube 117 dislodges particles on the passenger's handsand draws the particles in through the collection holes on the grips 115of the hand sampler 110. In one implementation, the hand-sampler 110 maymove in two motions. Specifically, in the first motion, the handle-barmay traverse 30-90° of a circumference of a circle vertically downwardfrom the position shown in order to rotate the surface area of the grips115 with respect to the surface area of the hand(s) pushing down. In thesecond motion, the handle-sampler 110 may traverse 60-90° of acircumference of a circle horizontally from the position shown. Thefirst and second motions may occur concurrently or separately.

As the passenger moves through the turnstile, the torso sampler 120brushes against the waist/torso area of the passenger, and suction inthe interior of tube 125 dislodges particles from the passenger's waistand draws the particles in through the collection holes 127 of the waistsampler 125. In one implementation, the torso sampler 120 traverses60-90° of a circumference of a circle horizontally outward from theposition shown, similar to the hand sampler 110. The combination of themovement of the hand and torso samplers 120 present the entrance 107which enables the passenger to traverse the collection device 100.

While the passenger moves and/or traverses the hand and torso samplers110 and 120, the shoe sampler 130 directs a stream of air from an outletport 134 (shown in FIG. 1B) to an inlet port 135. Specifically, thestream of air moves towards the passenger's shoe/pant cuff area todislodge particles and, with the dislodge particles, is drawn into theshoe sampler 130 through the inlet port 135. The hand sampler 110 andtorso sampler 120 may both be locked closed and only unlock when certainconditions are met. In one implementation, the outlet port 134 is on theright pedestal 106, while the inlet port 135 is on the left pedestal105. The air streams from the samples 110-130 are joined inside thepedestal 105 through “Y” type connections so as to enable the threesamplers 110-130 to impact on the sample media simultaneously asdescribed with respect to FIG. 3.

The collection device 100 may include a pressure switch on the floorjust before the entrance to the turnstile, or a proximity sensor at theentrance to detect the presence of the passenger. A detected presencemay control system components, such as, for example, the status of ablower, or the locking or unlocking of the hand and torso samplers 110and 120.

Components of the system may be constructed using a variety ofmaterials, such as, but not limited to, aluminum, steel, glass, plasticor composite. Metals such as aluminum or steel may interfere with theoperation of standard walk-through metal detectors if they are in closeproximity to the collection device 100. Composite or plastic materialsmay be used to avoid such interference.

In one implementation, the target sample rate is about 360 passengersper hour through the system, corresponding to 6 passengers per minute.This rate is determined by three main factors. One factor is the timetaken takes by the passenger to pass through the turnstile.

The second factor is the analysis time, which includes the time requiredto transport the sample to the analyzer, the time required for analysisof the material, and the time required to calculate results using thedata produced by the analyzer. In some implementations, the analysisfunctions may be operated in a pipelined manner such that, for example,a first sample is analyzed while a second sample is being collected andtransported to the analyzer.

The final controlling factor is one of choreography. For example, if theturnstile is capable of accepting a passenger every five seconds, tomaximize efficiency, the passengers need to present themselves to theturnstile in that amount of time.

Referring particularly to FIGS. 1B and 1C, internal components of thecollection device 100 include a blower 155 operating in a vacuum mode, amulti-area trace particle sampling and transport mechanism 160, acollection system 165, a detection unit or detector 170, retractablewheels 180, a computer system 185, a power supply 190, a carousel wheel195, and a detection unit 197. Other implementations of the collectiondevice 100 may include other components, such as, for example, aboarding pass reader, a wireless link unit, or a system controllerincluding a TCP/IP interface to an airport security network.

The blower 155 provides the necessary vacuum to operate the samplers110-130 and may be on continuously during operation of the collectiondevice 100, or may include a “standby” mode in which the blower isturned on when activated by the operator, or when a passenger sensorsenses a passenger approaching or entering the turnstile. The specifictype of blower 155 may be selected depending on desired parameters suchas required output, power consumption, or noise level. The blower 155may be a high quality regenerative blower, such as, for example, theGast Regenair Model R3105-12. In one implementation, a second blower isused to generate the air flow for the shoe sampler 130.

The multi-area trace particle sampling and transport mechanism 160 isenabled by efficiently transporting trace explosives particles downtubing to a collection system 165 without significant loss to theinterior walls of the piping. Small particles of explosives are known tobe unusually “sticky,” as the explosive crystals are often coated inoils, waxes or polymers. One way to prevent the particles from sticking(or at least to reduce the number of particles that stick) is tominimize the number of particles that reach the interior surfaces. Thismay be accomplished through design parameters such as, for example,maintaining proper velocity (e.g., greater than 10 m/s) within thetransport piping, using gentle bend radii (e.g., greater than 8 timesthe diameter of the pipe), and having inlet holes that that are sized tocreate a vacuum effect. Additionally, inside surfaces should be smoothand free of abrupt transitions. In one implementation employing theabove parameters, particles ranging in size from 5 to 300 microns may beentrained in a flow with a Reynolds Number between 10,000 and 50,000,with near 100% transport efficiency.

The collection system 165 is used to gather transported materialparticles so that the material may be analyzed by the detector 170.Various collector systems 165, such as a carousel wheel or reel-to-reelribbon system, which has multiple sample media collection stations orportions, may be used. In the collection system 165, the material isgathered on a sample media that is presented to the detector 170 foranalysis. During gathering, the collection system 165 may be sealedagainst the collection material.

One implementation employs contamination controlling software thatcontrols positioning of the sample media such that, if a given stationor portion of the sample media is deemed contaminated, that station orportion is skipped until cleaning or replacement of the sample media.Depending on implementation, the sample media needs to be replaced orcleaned at different intervals (e.g., daily or monthly).

As noted above, the collection device 100 also includes retractablewheels 180, a computer system 185, and a power supply 190. Theretractable wheels 180 are used to simplify transportation of theturnstile 175. The wheels may be raised (i.e., retracted into the wallsof the device) by use of one of several mechanisms, such as a jackscrew,a cam-lever, or a hex-bolt.

The computer system 185 may include a single CPU or multiple computers.In an implementation including two CPUs, one CPU is directed tocontrolling the turnstile system 100, and the second CPU is directed toanalyzing data. Included in the computer system 185 are applicationspecific boards such as an I/O (input/output) digital controller with anintegral A/D (analog/digital) and D/A (digital/analog) converter such asdevices manufactured by National Instruments. A monitor and keyboard maybe included to accept user input or for service and maintenance. In oneimplementation, a small LCD VGA monitor with either a touchscreen or akeyboard is permanently connected to the computer system 185 and placedbehind an access panel.

To enable compatibility with various supplied voltages, the line voltagemay be converted by the power supply 190 to feed DC components. In oneimplementation, the power supply 190 operates to convert 110/220 VAC,50/60 Hz to the required output(s). A small UPS (uninterrupted powersupply) may be included to enable completion of any sampling or analysisin progress if a power failure occurs, as well as to enable a clean shutdown of the computer system 185 in the event of a power failure.

The collection device 100 may further include a carousel wheel 195 anddetection unit 197. The carousel wheel 195 includes a sample mediaconfigured to hold the sample material as described with respect to FIG.4A. The detection unit 197 analyzes the sample material on the samplemedia as described with respect to FIG. 4B.

Referring to FIG. 2, an exemplary hand sampler 110 includes collectionholes 210 and hole contours 220. The hand sampler 110 may be used in thedevice 100 of FIGS. 1A-1C. In the hand sampler 110, trace sampling ofhand(s) occurs as the passenger moves the handle-bar on the hand sampler110.

The hand sampler 110 has a right and left hand section which may eachinclude collection holes 210 to vacuum the hand during the samplingprocess. In certain implementations, each of the two sections also mayhave a conductivity meter to determine that the passenger is using bothhands to hold the hand sampler, and that the passenger is not wearinggloves. Since it is desired to have some wiping motion to create sheerand pressure forces between the handle-bar and the hand of thepassenger, the design is such that the passenger needs to push thehandle-bar down, in a motion similar to that typically used, forexample, to unlock the brakes of luggage carts at airports. Thehandle-bar may move downward along an arcuate path, such that thehandle-bar rotates with respect to a downward pressing hand. Both themechanical motion of pushing the handle-bar down and a conductivitymeter reading indicative of skin may be required to unlock the handsampler 110 and torso sampler 120 allowing them to rotate and thusallowing the passenger to pass through the collection device 100.

Air and particles suspended in the air are drawn in for collection anddetection through the collection holes 210. As explosive particles maybe wedged in rough surfaces (e.g., skin or clothing), the hand sampler110 is designed to place a pressure and shear force on a passenger'shands concurrent with the intake of dislodged sample material. The holecontours 220 are shaped to ensure an appropriate pressure and sheerforce is generated locally around the collection holes 210. In oneimplementation, the hole contours 220 are flared or “V” shaped such thatthe effective collection area is larger than the diameters of thecollection holes. The edges of the hole contours 220 or collection holes210 may be sharp, abrupt, or otherwise shaped to facilitate a scrapingmovement. As with all three samplers 110-130, the number of collectionholes 210 on the hand sampler 110 is a design feature and may varydepending on desired characteristics. In particular, more or largercollection holes 210 increases the amount of gathered material foranalysis while also increasing the size and power requirements of theblower(s).

As particles are dislodged, they are vacuumed into the system. Ahand-release mechanism on the gate is designed to ensure contact withthe finger tips, and the downward pressure applied to the hand baroptimizes the sampling conditions. Optionally, a protective panel abovethe hand bar houses a UV sterilizer 172 as shown in FIG. 1C, and alsoserves to ensure that the bar may only be pushed with the hand, and notwith the elbow or a handheld item.

One particular implementation includes a 6 mm inner-diameter hole at theend of the hand sampler 110 to develop at least a 10 m/s linear gasvelocity inside the hand sampler 110. The sampling section hascollection holes 210 which may be angled at 45° to the direction of flowfor each hand. Depending on implementation, the grip may be operatedwith one or both hands. Each collection hole 210 is at the apex ofapproximately 1 cm wide and 1 cm long V-shaped hole contour 220. Eachhole has about 1.5 mm inner-diameter, with the velocity at the holebeing 105 to 110 m/s, and the linear velocity in the pipe being 10 to 15msec. The flow in the pipe is turbulent with a Reynolds number of from15,000 to 22,000.

Trace sampling of the waist/pocket area occurs as passenger pushes thetorso sampler 120 open with the body. The torso sampler 120 may belocked until movement or a conductivity reading of the hand sampler 110triggers unlocking. As shown, the torso sampler 120 includes an ovalshaped gathering tube and a planar surface. Other implementations of thetorso sampler 120 may employ different shapes. For example, thegathering tube may be a “U” shaped, and the surface may be curved orotherwise formed to conform to the shape of a body. The torso samplermay include a series of collection holes that are the same or similar tothe collection holes 210 on the hand sampler 110. The torso sampler 120uses close-coupled vacuuming of the clothing surface while applying ashear force. This is achieved by having the passenger push against aswinging tubular door, with the vertical tube section of the door beingdesigned to come into close contact with the body so as to sample theregion between mid torso and thighs.

As with the hand sampler 110, particles that are in the path of thecollection holes 210 will be mechanically dislodged by the shear forceand applied pressure of the lip edges, and then sucked into thecollection holes. As the passenger moves past the gate, the verticalpart of the tube scrubs the torso from the center of the body to theside, covering about 25% of the total torso surface area.

In one particular implementation, the vertical section of the torsosampler 110 is 50 cm tall, with 18 collection holes. Each collectionhole 210 is 1.5 mm in diameter and located at intervals of 1 cm, with a0.2 cm rounded lip on each V. Each orifice is at the apex of a 1 cm wideand 1 cm long V-shaped indent. The flow velocity at each orifice isbetween 59 and 110 msec. This is sufficient to entrain particles in the5 to 200 micron size range, without entraining larger particles andhairs. The linear velocity inside the pipe is 10 to 28 m/s. As with thehand sampler, the flow inside the 1 inch diameter pipe is turbulent witha Reynolds number in the 14,000 to 41,000 range.

Both the hand and torso samplers 110 and 120 may be spring loaded toplace a resistance of about a few pounds against the passenger. If apassenger moves past the samplers 110-130 too quickly, an insufficientsample may be collected. Optionally, speed of a passenger may be slowedby designing a resistance system that increases exponentially withspeed. In particular, a hydraulic or pneumatic resistance system may beincluded to provide low resistance with slow movement and highresistance with quick movement. Further, the torso sampler 120 mayinclude a significantly higher resistance than the hand sampler 110 atany speed to encourage use of the passenger's torso, rather than thepassenger's hands, to push the gate.

In the shoe sampler 130, trace sampling of the shoes and pant cuffsoccurs while the passenger stands at the turnstile entrance and beginsto pass through the gate. The sampling is conducted by gatheringparticles from an air stream that is blown out of one or more holes(e.g., the outlet port 134) on one side of the turnstile passage andsucked in through one or more other holes (e.g., the inlet port 135) onthe other side of the turnstile passage. In one implementation, anair-knife less than 1 cm in width and 15 cm in height, with a flow rateof 4 liters per sec (Us) is used to dislodge particles from shoes, bootsand pant cuffs, as the passenger walks through the turnstile. Theair-knife has benefits over a “puff” based blowing system, in that thegathering ability is continuous and less susceptible to missing areas ofpassengers. The particles are drawn into the air and then sucked into avacuum-line at a flow of 6.5 l/s by means of 4 sampling ports of 6 mminner-diameter. Tapered lower sidewalls of the turnstile minimize thedistance between the air-knife and the shoes/pant cuffs, and thedistance to the sampling inlet. The air jet and intake ports arepositioned to maximize particle collection efficiency.

Once the passenger has completely passed the collection device 100, thehand sampler 110 and torso sampler 120 return to the original startposition. Spring loading that is dampened to insure that these twocomponents do not slam shut may be included. After completion of thesampling, the collection device 100 analyzes the sample and may presentthe results to the operator as either “Clear” or “Alarm.”

The previous descriptions provide exemplary implementation of adetection system 100 including a hand sampler 110, a waist/torso sample120, and a shoe sampler 130. Other implementations may include differentfeatures, such as a pressure sensor to detect performance-limiting holeblockage and to automatically prompt a cleaning cycle upon detection ofsuch blockage. Also, sensors (e.g., optical sensors) may be employed todetect passengers climbing, crawling, or otherwise avoiding thesamplers. Further, a camera may be included that may take pictures ofall passengers or only passengers that test positive for certainmaterials.

Referring to FIG. 3, an impact collector 300 combines the air streams ofthe three samplers into a single air-stream from which particles arecollected onto a sample media 320. There is a critical flow to avoidparticles falling out of the airflow and onto the tubing walls. Oneimplication of particles falling out of the sample stream is a loss ofsample that leads to a false negative. Another implication is one ofcarry over. Specifically, if a particle falls out of the sample stream,it has the potential of showing up in later samples leading to a falsepositive. Because of such implications, after every positive sampling,there may be a clearing purge cycle, where the system is run withoutadditional sample material.

In the impact collector 300, the end of the sample tube may be closecoupled to the sample media 320. The sample media may be constructed outof a variety of materials, such as, for example, Teflon, stainless steelmesh, carbon fiber, or a deactivated glass wool pad. If resistiveheating is being employed, the sample media 320 may need to beconductive. If radiative heating is being employed, conductivity of thesample media 320 is not required.

In the impact collector 300, the air and explosive vapors divideaccording to the ratio of the bypass flow to the collector flow. Typicalcollector flows are between 0 and 10 percent of the total flow.Particles, however, are not able to make the 180° turn 310 and thusimpact upon the sample media 320. In order to keep the piping of theturnstile clean, valves may be placed downstream of the collectionsystem and kept closed except during the sampling time.

In one particular implementation, the internal inner-diameter of theimpact collector 300 is about 1.5 cm. The outer ring is about 3 cm indiameter. If the sample media 320 rotates, the impact collector 300itself needs to clear the sample media 320. The impact collector 300 mayneed to seal against the portion of the sample media 320 at the outerring with the inner tube being from about 0.2-2.0 cm away from thesample media 320. An O-ring may be included on the outer tube to form aseal. In come cases, slight leakage may be acceptable. Depending onimplementation, either the impact collector 300 is lowered to form theseal, or the sample media 320 itself is raised to form the seal.

Referring to FIG. 4A, a top view of a collection system 400 includes theimpact collector 300 and sample media 320 of FIG. 3, and a detectionunit 430. In the collection system 400, the impact collector 300 is usedto deposit the gathered material onto the sample media 320. The mediamoving mechanism moves the sample media 320 such that the sample mediaincluding the deposited material moves from a region adjacent to theimpact collector to a region within the detection unit 430. Thedeposited material is than analyzed for traces of specific material.

Referring to FIG. 4B, a side view of a collection system 400 includes amedia moving mechanism 440, a heating controller 450, and contacts 460.The discussion below refers to two specific implementations directed toresistive and radiative heating exothermic decomposition (with resistiveheating shown in FIG. 4B), but other methods of initiating thermaldecomposition may also be used. In particular, elevating the temperatureof a particle by using electromagnetic radiation, lasers, the convectionof heat via warm air to the particle, or the conduction of heat to theparticle would be sufficient for causing thermal decomposition.

The particular collection system 400 to be used may be based on factorssuch as a desired period between maintenance sessions, ease ofmaintenance, or cost. FIG. 4 illustrates an implementation involving acarousel wheel 410 with a reusable discreet sample media 320. Otherimplementations, such as a “reel-to-reel” system with a one time orreusable sample media 320, also may be used. Such a reel-to-reelmechanism may be more costly to build and more difficult to maintain(e.g., by replacing the worn sample media 320) than the carouselmechanism of 400. Because the reel-to-reel mechanism could hold moresample media, the time between replacements would be greater than forthe carousel implementation.

In the illustrated implementation having a carousel wheel 410, thesample media 320 is within the carousel wheel 410 and includes either aseries of discreet collecting areas or a continuous collecting area. Ina series of steps, the collection system 400 gathers collected materialonto an area of the sample media 320 and then rotates to a detectionunit 430 to enable the deposited material to be analyzed by a detectionunit to detect the presence of particles of materials.

According to various implementations employing the carousel wheel, afirst station is the impact collector 300, which may seal to thecarousel wheel 410. The term “station” refers to specific locations ordegrees of rotation of the carousel wheel 410. The position of stationsmay be determined by the position of holes along the circumference atangular positions of the carousel wheel 410. After particles aredeposited with the impact collector 300 to an area of the sample media320, the carousel wheel 410 rotates to the second station, which is thedetection unit 430. Characteristics of the detection unit 430 depend onthe detection unit employed. If the detection unit is a thermaldesorber, the detection unit may clamp over the gathered material whichis vaporized.

The actual detection unit chosen may vary based on desiredcharacteristics, such as complexity, cost, or sensitivity. Variousdetection units may be employed, such as an ion mobility detector (IMS),gas chromatography coupled with a chemiluminescence detector (GC-CL), athermal desorber, a resistive heating exothermic decomposition detector,or a radiative heating exothermic decomposition detector.

A media moving mechanism 440 is employed to rotate the sample media 320,and in the implementation discussed above, the carousel wheel 410. For ahigh degree of positional accuracy, a stepper motor may be employed. Asa stepper motor is expensive and requires specialized electronics tocontrol, a simpler alternative that may be used is a unidirectional orbidirectional DC motor. An LED optical sensor may be used to determineand control the position of the media moving mechanism 440. Maintenanceof the carousel wheel 410 may be conducted through an automatic discloading and unloading station to extend the time between routinereplacement of the sample media to, for example, one month.

In one implementation that includes a resistive heating exothermicdecomposition detector (discussed below), the sample media 320 area isthree cm² and includes two contacts 460 which are placed at oppositeends of the sample media 320. The contacts 460 may be shaped in variousways, such as, for example, raised metallic bumps (e.g., like a contactfor a battery), rods, or plates. A spring loaded contact may be used tocomplete the connection. The sample media 320 may be designed with upperand lower halves. In one assembly method, the two halves are separated,the sample media 320 is installed on the bottom half, and the top halfis attached on top of the sample media 320 forming a sandwich. In oneimplementation, for each portion of the sample media 320, one of thecontacts 460 is in the form of an electrode which is tied to a singlecommon connection point (not shown), and the other contact 460 is aunique connection (as shown in FIG. 4B). In such an implementation, thecommon connection point is constantly connected to the power supply, andonly one unique connection is connected at a time to enable only oneportion to be resistively heated. The sample media may include holes forthe optical sensors (or LED sensor as discussed above with respect tothe carousel wheel 410 implementation).

Residual material, such as oils, may contaminate or mask latermeasurements, or may shorten the life of a reusable sample media 320. Byheating the sample media 320 to a higher temperature than that requiredto trigger decomposition of energetic material, such residual materialmay be burned off. Optionally, a high temperature bake out attemperatures in excess of 300° C. may be conducted at the second stationor a separate third station in order to thermally decompose remainingparticles. A bake out at a third station may be particularly useful inimplementations without resistive or radiative heating, such as an IMSor GC-CL system with thermal vaporization.

In one implementation, the real-time temperature of the sample media 320is measured through a pyrometer, and such measurement is a part of afeedback loop to enable the temperature to be actively controlled. Thepyrometer may be included in the detection unit 430 or the heatingcontroller 450. During heating, there is slight expansion of the samplemedia 320. In order to prevent distortion, the design is such that thereis a slight tension on the sample media 320.

Detecting trace amounts of explosives remains a challenging task andoften suffers from poor sensitivity to minute amounts of explosives andlow throughput. These issues can be addressed by relying on the rapidkinetics and thermodynamics associated with the thermal decomposition ofexplosives. Although most molecules decompose endothermically whenheated in an atmosphere deprived of oxygen, an explosive compounddecomposes exothermically releasing heat to the environment. Thereleased heat is immediately transferred to the molecules surroundingthe decomposing explosives, which results in a localized increase intemperature that provides a measurable indicator of an explosivecompound.

Specifically, explosive compounds decompose exothermically (they releaseheat to the surroundings) when heated anaerobically. If the mass of theexplosives is large enough, the temperature rises, which accelerates thereaction rate even further, releasing additional heat, and culminatingin a runaway thermal explosion. For sub-critical masses, the material isconsumed before it explodes as heat is lost to the surroundings.Nevertheless, even for these sub-critical cases, the temperature risesabove its surroundings before decaying back to the ambient.

A resistive heating exothermic decomposition detector senses the thermalenergy released during exothermic decomposition, which is athermodynamic property unique to energetic materials. This feature makesit possible to detect explosives, including nitro-organics andnitro-salts, peroxides, perchlorates, and gun powder, as well ashomemade explosives of as yet unknown composition.

The heat released from small amounts of explosives during decompositionmay be detected by using the IR detection array to detect the thermalsignature resulting from this process. The camera is configured todetect heat in the mid-wave infrared (MWIR), 3 to 5 micron wavelength,or long-wave infrared (LWIR), 8 to 12 micron wavelength, regions toobserve the temperature of the environment surrounding an explosiveparticle. Thermal imaging cameras employing detection in the MWIR regionbenefit from superior resolution and contrast while those detecting inthe LWIR region offer enhanced sensitivity to smaller temperaturefluctuations and are less affected by atmospheric conditions (e.g., LWIRradiation can be transmitted through mist and smoke).

For trace explosive decomposition, the inherently small particle sizescomplicate the detection process. For an explosive compound undergoinganaerobic thermal decomposition, the heat released is expected to beequivalent to about a 100° C. temperature rise in a 200° C. environmentwithin a five to five hundred millisecond time frame, depending upon thetype of explosive, its mass, the heating rate and the rate of heat loss.In some cases, the time frame is 5 to 30 milliseconds. If all of theexothermic energy produced by the decomposition of the explosiveoccupied one instantaneous field of view (IFOV) of the IR detectionarray, this would be easily detectable, since most MWIR/LWIR camerashave sensitivities near 0.05° C. However, trace amounts of explosiveparticles emitting this heat weigh as little as a few nanograms andtheir emitted energy would only occupy a region 0.1 to 0.01 millimetersin diameter. Since the IFOV per pixel of a typical camera lens is abouttwo millimeters in diameter at close range (approximately one foot awayfrom the source), the released energy from a trace explosive isundetectable across the IFOV area. In this case, the temperature risehas been diluted across the entire IFOV and appears as a temperatureincrease as small as 0.003° C. for a nanogram-size particle.

In order to detect localized heat signatures, the IR detection array isappropriately configured to record fast, microscopic reactions. Becauseof these constraints, the camera has a macro (close-up) lens capable ofachieving an IFOV of less than between 50 and 150 microns in diameterper pixel. In addition, the resolution of the camera is sufficient toprovide numerous individual pixels which act as their own individualheat detectors and serve to increase the sensitivity of the detection ofenergetic particles. For example, doubling the resolution of a thermalimaging camera leads to a ×4 to ×8 lowering of the lower detection limitof this method. Using a camera with a sensitivity of 0.05° C., a traceexplosive decomposition could be easily detected with a signal to noisesomewhere between 100 and 200 (with a signal to noise of 40 as the videothreshold for the human eye). A final technical challenge arises due tothe speed of the thermal decomposition process. If the cameraintegration time between frames is long relative to the energy release,the energy is time averaged and may not be captured by the camera. Forexample, for a five to ten millisecond reaction and using a 60 Hz (16ms) imaging rate, the observed energy released from an energeticparticle is reduced by less than a factor of 3. This yields a signal tonoise ratio somewhere between 40 and 80.

In one implementation, the IR detector array is a long wave infra reddetector (LWIR) that is sensitive in the 7.5 to 14 micron range. Thedetector is equipped with a focusing lens in order to resolve pixelsdown to about 50 microns. The refresh rate of the system is 60 Hz. Thedetector is a 320×240 array with 76,800 pixels. The sensitivity of eachpixel is specified as 0.05° C., which facilitates sensitivity at themid-picogram level. Since the particle mass is inversely proportional tothe third power of the pixel size, the sensitivity can be enhanced byusing a more powerful focusing lens.

Analytical interpretation of the results is possible by examining thetemperature of individual pixels or the average of several pixels as afunction of time. Results may demonstrate that a particle's rapidincrease in temperature exceed that of the sample media 320. Thisfeature can be used in algorithms to automatically detect the presenceof explosives. In particular, each energetic compound has a quantifiableand positive heat of decomposition (H) and a quantifiable activationenergy (E). H impacts the total heat that is released and E the rate ofheat release. These two properties interact in such a way that adetector may distinguish classes of explosives and/or the chemicalcomposition.

Automatic algorithm based target recognition is used to track multiplepixels simultaneously and to automatically recognize the uniquecharacteristics of explosives. Simple enhancements include subtractionof the varying background temperature, and displaying the differentialso as to better visualize the peak maximum. Local maxima in atemperature versus time plot are indicative of the presence ofexplosives and are mathematically defined as points at which the timerate of change of the temperature equals zero (i.e., dT/dt=0). However,both local maxima due to the fluctuating temperature of the sample media320 may also be present. To correct for these artifacts, the samplemedia 320 temperature may be subtracted from the temperature recorded atvarious points.

Specifically, in one implementation, the analysis of the samplecollected on the sample media 320 may be performed by heating thecollection area from ambient to about 300° C. in one to two seconds.This heating may be performed in front of the IR detection array(included in the detection unit 430) one implementation of whichincludes 320×240 pixels focused on the sample area. Each pixel may viewabout 100 μm square for a total viewing area of about 2.5×1.5 cm. Whenthe sample media 320 is rotated to the second station, which includesthe detection unit 430, heating is performed resistively with about 10amps at 2 volts.

In a radiative heating implementation, a flash lamp is included in theheating controller. The heating controller 450 and the detection unit430 may optionally be on the same side of the sample media 320. Theflash lamp delivers the necessary activation energy for initiatingdecomposition of residual explosive particles.

The previous description provides exemplary implementations of acollection system 400 and a detection system 450. Other implementationsmay include different features, such as a checking solution injectedonto the sample media 320 on an infrequent but scheduled basis to testthe ability of the system to successfully detect particles of amaterial. This mechanism may include a reservoir, that needs to bereplaced monthly, and may include either the LEE miniature variablevolume pump model number LPVX0502600B, (see www.theleeco.com) or a smallKNF model UNMP830 (see www.knf.com) or similar pump and a LEE solenoidvalve similar to LEE model number INKX051440AA.

FIG. 5A shows data results 500 of exothermic decomposition detection. Inparticular, a picture is shown of a sample media with a decomposingmaterial at four different instances of time. Specifically, data results500 for the energetic detection of a particle of smokeless powder usinga 60 Hz frame rate are shown. Element (a) shows an initial IR image atframe 110 with a relatively cool particle and filament. Next, element(b) shows an IR image at frame 389 showing elevated temperatures aroundthe particle just prior to explosion. Next, element (c) shows an IRimage at frame 390 showing the particle explosion. Finally, element (d)shows an IR image at frame 391 showing elevated gas temperaturesresulting from the particle explosion.

Referring to FIG. 5B, data results 550 for the same decomposition areshown from the perspective of a pixel viewing the smokeless powder and apixel viewing the sample media across time. In the results, the fourinstances of time from the results 500 of FIG. 5A are marked.Specifically, a two-dimensional plot of the thermal signature of onepixel near a smokeless pellet and one pixel on the sample media isshown.

Referring to FIG. 6, a method for detecting particles includes gatheringthe particles from one or more locations, depositing the gatheredparticles onto a sample media, rotating the sample media to a detectionsystem, and analyzing the gathered particles with the detection system.

Particles are gathered through collection holes (610). As shown in FIG.1, the collection holes may be distributed across a handle-bar, torsogate, a shoe blower, or other devices. The particles may be gatheredthrough multiple devices concurrently. In one implementation, apassenger pulls down a handle-bar which unlocks a gate that may bepushed with the passenger's torso, all while an air-knife blowsparticles from the passenger's shoes and cuffs. In particular, friction,pressure, and sheer force are produced by the resistance of thehandle-bar, torso gate, and air-stream, which releases dislodgedparticles for gathering.

The gathered particles are then deposited onto the sample media (620).If gathered from multiple locations, the particles may first be combinedinto a single stream of particles, and then the single stream may bedeposited onto the sample media as shown in FIG. 2. In oneimplementation, the sample media is reusable and may be moved after adeposition such that a different portion of the sample media ispresented for the next deposition.

The gathered particles are presented to a detection unit (630). If thesample media is within a carousel wheel, the carousel wheel is rotatedto present the portion of the sample media which includes the gatheredparticles to the detection unit. In one implementation, after eachdeposition, the carousel wheel is rotated, and after a number ofdecompositions, a portion of the sample media is reused.

The gathered particles are analyzed (640) by the detection unit. Eitherthe carousel wheel or the detection unit may heat or radiate thegathered particles to spur decomposition. In one implementation, acurrent is driven through the sample media to resistively heat thegathered particles while an IR detection array monitors particledecomposition.

The previous description provides exemplary implementations of a methodfor detecting particles. Other implementations may include differentsteps, such as, for example, a cleaning cycle may be run after everydeposition or analysis. The cleaning cycle may include heating and/orrunning an air-stream through part or all of the sample media.

1. A trace sampling detection system comprising: a gathering deviceconfigured to gather particles through each of: a handle-bar includingcollection holes positioned to be adjacent to a user's hand when theuser grips the handle bar, wherein the handle-bar is configured torelease particles in response to a grip and motion of the user, a gateincluding a series of collection holes positioned to be adjacent to theuser's clothing when the user traverses the gate, wherein the gate isconfigured to release particles in response to pressure applied from theuser, an air-stream gatherer including an outward vent and an in-drawingvent positioned to enable objects to be placed between the outward andin-drawing vents, wherein the air-stream is configured to releaseparticles from objects that block the air-stream between the outward andin-drawing vent; a collection tube configured to deposit gatheredparticles from the gathering device onto a portion of a sample media; acarousel wheel that includes the sample media and is configured torotate the sample wheel such that the portion of the sample mediaincluding the gathered particles is presented to an exothermicdecomposition detector; and an exothermic decomposition detectorconfigured to detect, through an infrared sensor, the decomposition ofthe gathered particles.
 2. The system of claim 1 wherein the collectionholes are tapered.
 3. The system of claim 1 wherein the collection holeshave edges configured to scrape a surface that contacts the edges. 4.The system of claim 1 wherein the handle-bar is configured to move in aradial motion.
 5. The system of claim 1 wherein the handle-bar includesa conductivity sensor configured to detect the presence of skin.
 6. Thesystem of claim 1 wherein the gate is shaped with a curve that isdesigned to conform to the shape of part of a human body.
 7. The systemof claim 1 wherein the gate will swing out only when the handle-bar ismoved.
 8. The system of claim 7 wherein the movement of the gatepresents a path for the user to traverse.
 9. The system of claim 1wherein the gathering device is configured to gather particlesconcurrently from the handle-bar, gate, and the air-stream gatherer. 10.The system of claim 1 wherein the analyzing system is configured todetect particles other than explosive particles.
 11. The system of claim1 further comprising a blower to create the vacuum in the collectionholes and the in-drawing vent.
 12. A trace sampling detection systemcomprising: a gathering device configured to gather particles throughtwo or more of: a handle-bar including collection holes positioned to beadjacent to a user's hand when the user grips the handle bar, a gateincluding a series of collection holes positioned to be adjacent to theuser's clothing when the user traverses the gate, an air-stream gathererincluding an outward vent and an in-drawing vent positioned to enableobjects to be placed between the outward and in-drawing vents; and ananalyzing device configured to analyze gathered particles from thegathering device for properties that are indicative of the presence ofparticles of explosive materials.
 13. The system of claim 12 wherein thecollection holes are tapered.
 14. The system of claim 12 wherein thecollection holes have edges configured to scrape a surface that contactsthe edges.
 15. The system of claim 12 wherein the handle-bar isconfigured to move in a radial motion.
 16. The system of claim 12wherein the handle-bar includes a conductivity sensor configured todetect the presence of skin.
 17. The system of claim 12 wherein the gatewill swing out only when the handle-bar is moved.
 18. The system ofclaim 12 wherein the movement of the gate presents a path for the userto traverse.
 19. The system of claim 12 wherein either the gate or thehandle-bar employs less resistance to movement for slow movements thanfor quick movements.
 20. The system of claim 12 wherein the gatheringdevice is configured to gather particles concurrently from two or moreof the handle-bar, gate, and the air-stream gatherer.
 21. The system ofclaim 12 wherein the analyzing system is configured to detect particlesother than explosive particles.
 22. A method of trace sampling detectioncomprising: gathering particles through two or more of: a handle-barincluding collection holes positioned to be adjacent to a user's handwhen the user grips the handle bar, a gate including a series ofcollection holes positioned to be adjacent to the user's clothing whenthe user traverses the gate, an air-stream gatherer including an outwardvent and an in-drawing vent positioned to enable objects to be placedbetween the outward and in-drawing vents; and analyzing the gatheredparticles for properties that are indicative of the presence ofparticles of explosive materials.
 23. A trace sampling detection system,comprising a gathering device configured to gather particles through oneor more collection holes; an impact collector configured to depositgathered particles onto a portion of a sample media; a carousel wheelwhich includes the sample media wherein the carousel wheel is configuredto rotate the sample wheel such that the portion of the sample mediaincluding the deposited gathered particles is presented to an exothermicdecomposition detector; an exothermic decomposition detector configuredto detect, through an infrared sensor, decomposition of heatedmaterials.
 24. The system of claim 23 wherein the carousel wheel isconfigured to heat the sample media resistively.
 25. The system of claim24 wherein the sample media is configured to be resistively heated byrunning a current through the sample media.
 26. The system of claim 23wherein the sample media is configured such that the same portion of thesample media may be reused through multiple exposures to the impactcollector and the exothermic decomposition detector.
 27. The system ofclaim 23 wherein the exothermic decomposition detector is configured toheat the sample media radiatively.
 28. The system of claim 23 whereinthe carousel wheel is configured to direct the sample media through areel-to-reel mechanism.
 29. A transportation mechanism for a tracesampling particle detection system which includes a gathering device, animpact collector configured to deposit gathered particles, and anexothermic decomposition detector configured to detect decomposition ofa deposited material, the transportation mechanism comprising: acarousel wheel which includes a sample media configured to accept adeposit of material from the impact collector, wherein the carouselwheel is configured to rotate the sample wheel such that the portion ofthe sample media including the deposited gathered particles is presentedto the exothermic decomposition detector.